We live in a galaxy that contains an estimated 200 billion stars, yes that’s billion with a ‘b’, and our galaxy is only one in a Universe of tens of billions, more likely hundreds of billions of galaxies. So there are a lot of stars out there yet only a few are known to the average person. In this post I’ll be talking about some of the latest discoveries about three of the best known stars starting with the most important star of them all, at least to us, our own Sun.
Even after 400 years of intense study our Sun still holds many mysteries. One of the biggest is the fact that the Sun’s atmosphere, the corona, the part we can only see during a total eclipse, is much, much hotter than the Sun’s surface, which we call the photosphere. Now we know that the Sun’s source of energy is the nuclear fusion of hydrogen into helium that takes place in the star’s core, at the very center, which is at a temperature of about 15 million degrees Kelvin. As that energy flows outward the temperature decreases until at the photosphere it’s only 5800 degrees Kelvin. However beyond the photosphere, in the corona the temperature suddenly goes back up to a million degrees Kelvin. The mystery is what is causing the corona to have such a high temperature.
Prior research had also discovered a similar phenomenon. The solar wind, the charged particles that flow out from the Sun and which cause the Aurora if they strike the Earth, are actually moving rather slowly when they are close to the Sun but accelerate as they move further away. The question once again is, where is the energy coming from to cause that acceleration?
Now both the particles in the corona and those in the solar wind are charged subatomic particles, electrons and protons, a state of matter that is known as plasma, and unlike neutral atoms they are greatly effected by electromagnetic forces. Therefore astrophysicists have long theorized that it was the Sun’s magnetic field that was supplying the energy via a type of electromagnetic wave called Alfvén waves. The precise details of how the process worked however were difficult to work out without measurements from within the corona itself. In fact two sets of measurements would be required at the same time, one from close to the Sun and the other from a considerable distance further away in order to see if the magnetic field dropped in strength as the solar wind increased in velocity.
Recently two separate space probes, NASA’s Parker Solar Probe, the closest man-made object to the Sun ever, and the European Space Agency’s Solar Orbiter were in just the right position to take those measurements. Parker was orbiting the Sun at a distance of just about nine million kilometers, again that’s the closest any man-made object has come to the Sun, and was making a series of measurements that included both the density and velocity of the particles in the solar wind as well as the strength of the Sun’s Magnetic field along with the fluctuations caused by the passage of the Alfvén waves.
Two days later the same section of the solar wind that Parker had measured flowed past Solar Orbiter and it took the same set of measurements. Upon examination what the two sets of data showed was that the strength of the magnetic field had dropped to almost nothing while the speed and hence temperature of the solar wind particles had increased. Precise calculations showed that the transfer of energy was balanced; the magnetic field had lost exactly the same energy that the solar wind had picked up. Like zillions upon zillions of tiny surf boards the protons and electrons had ridden the crests of the Alfvén waves and gained energy in the process.
Whether or not other stars also have magnetic fields that produce Alfvén waves that drive their solar wind is unknown at present but little by little we are learning more about them. One of the best known stars, if only because of that movie, is Betelgeuse, a gas giant star that resides in the constellation Orion. Betelgeuse is also somewhat famous because astronomers think that sometime in the next million years or so it will explode as a supernova, shining so brightly that it will be visible during the daytime.
In fact just about five years ago Betelgeuse suddenly dropped significantly in brightness and rumours began on the internet that was star was getting ready to explode. Astronomers themselves were more cautious however; Betelgeuse’s brightness was always known to vary, although this degree of dimming was unusual. Over last few years Betelgeuse’s brightness has fluctuated and astronomers have concluded that a large dust cloud near Betelgeuse is occasionally covering much of the star’s disk causing the dimming event.
Now a new paper by lead author astrophysicist Jared Goldberg at Flatiron University in New York City has proposed an alternate solution, Betelgeuse has a companion star just a bit more massive than our own Sun. Based upon measurements made of the star’s brightness over the last century astronomers had found that Betelgeuse had not only a fundamental period of oscillation of 416 days that was caused by an expansion and contraction of the star’s radius but an additional long secondary period of about 2170 days.
Dr. Goldberg asserts that this secondary period is caused by the orbit of a companion star 1.17±0.7 the mass of our Sun. This companion star orbits around the more massive Betelgeuse at a distance that is about 2.4 times Betelgeuse’s radius. Betelgeuse is so huge that if placed where our Sun was it would swallow all of the inner planets out to and including Jupiter. It is when this companion star is behind Betelgeuse that we see a dimming of the brightness of the two stars.
Dr. Goldberg and his team may be right, and if they are then we may be wrong about our estimate as to how long before Betelgeuse goes nova, the star may have quite a few million years left to it. On the other hand if the dimming we have observed recently is caused by disturbances in the star’s outer atmosphere then time may indeed be running out for Betelgeuse.
Another very familiar star is the North Star or Pole Star Polaris. As I mentioned in my post of 19August 2024 Polaris is a member of a class of stars known as Cepheids whose rhythmic oscillation in brightness allows astronomers to use them as distance markers. Polaris in particular brightens and dims ever four days.
Polaris has made a bit of news lately because for the first time astronomers have succeeded in producing a rough image of the star’s disk. Now this is really a big deal, even in some of the biggest telescopes the very closest stars are still nothing but a point of light. The technology to resolve, as astronomers put it, another star’s disk has only been developed over the last twenty or so years and still requires a lot more work than just taking a picture. In fact astronomers had to combine the light gathered by six telescopes into a single instrument in order to resolve Polaris’ disk.
And the astronomers who took Polaris’ picture were actually trying to confirm the existence, and learn more about a suspected second companion star to Polaris. The North Star was already known to have a companion star at a large distance from the main star but it was in 2005 that the Hubble Space Telescope discovered that Polaris also had a second much closer and smaller star orbiting it as well. In order to learn more about this second, much closer companion astronomers needed the greater resolution that could only be obtained by combining the light of several telescopes, a technique known as Interferometry. This technique also allowed the team to produce the image of Polaris’ disk, which shows large spots or blotches on the star’s surface, perhaps something akin to the sunspots on our Sun? Anyway, it’s nice to know that even as astronomers push ever farther into the depths of the Universe they are still learning more about some of the stars we humans have gazed at for thousands of years.
